Journal of High Pressure Institute of Japan
Online ISSN : 1347-9598
Print ISSN : 0387-0154
ISSN-L : 0387-0154
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Original Paper
  • Yutaka TSUCHIDA
    2020 Volume 58 Issue 1 Pages 4-13
    Published: 2020
    Released: February 29, 2020
    Low cycle fatigue tests were conducted on industrial pure iron (electromagnetic soft iron) after hydrogen pre-charging. The effect of hydrogen on fatigue life was examined, in combination with stress response during monotonic and cyclic straining. The hydrogen desorption behavior was determined by thermal desorption analysis (TDA) on specimen interrupted at 10, 30 or 100 cycles with hydrogen post-charging. Comparing to the results without hydrogen pre-charging, the effect of hydrogen pre-charging was discussed. The hydrogen pre-charging degraded the fatigue life down to 1⁄8. Although the upper and lower yield strengths became lowered by hydrogen pre-charging, the stress range during cycling exceeded that of without hydrogen pre-charging. The amount of hydrogen that were trapped by either dislocation, grain boundary, vacancy or vacancy cluster tended to increase with strain cycling, with⁄without hydrogen pre-charging. Hydrogen pre-charging prompted the appearance of hydrogen that was trapped by vacancy and vacancy cluster. The hydrogen trapped by vacancy cluster was most of all affected by hydrogen pre-charging and strain cycling:It could be correlated with the fraction (N⁄Nf) , where N is number of interrupted cycles and Nf is that of fatigue life. The reduced yield strength with hydrogen pre-charging may be caused by substitution of carbon atoms by hydrogen atoms, which are interacting with dislocation. The increased stress range during cycling may be originated by hydrogen coupled with fresh born vacancy to suppress the mobility of dislocation.
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  • Keisuke MORI, Chobin MAKABE, Shinji ANDO, Shin-ichi INOUE
    2020 Volume 58 Issue 1 Pages 14-21
    Published: 2020
    Released: February 29, 2020
    Fatigue crack growth tests of rolled magnesium alloy AZ31 were performed with a side-notch plate specimen under negative mean stress conditions. In the results of the present study, even if the experimental conditions were the same, the crack growth behavior varied depending on the condition of the specimen and depending on the microstructure. The local friction between large size and small size crystals and the shear deformation are expected to be related to the crack closure. The crack growth rate was affected by the crack opening stress. When the crack growth rate was lower level, the crack closure behavior worked due to the plastic deformation and the roughness of the fracture surface. There was local rough pattern which work as the shear lip at sides of the crack surface.
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  • Takuya MATSUZAKI, Hidekazu MURAKAWA, Ninshu MA, Seiichiro TSUTSUMI, Ka ...
    2020 Volume 58 Issue 1 Pages 22-38
    Published: 2020
    Released: February 29, 2020
    In our previous study, it was shown that the fatigue life of the boxing fillet welded joint was enhanced by about 10 times by applying the elongated bead welding with 40 mm bead length to the welded joint by using low transformation temperature (L. T. T. ) welding material.
    In this study, to investigate practical use of the elongated bead welding with L. T. T. welding material, the followings were discussed, (1) The estimation of the residual stress distribution of boxing fillet welded joint to which the elongated bead welding with L. T. T. welding material was applied, (2) The work load and time of elongated bead welding on site welding, (3) The fatigue life enhancing effect of two elongated bead welding joints using different L. T. T. welding materials, L. T. T. 10Cr-10Ni filler metal (LTT1) and L. T. T. 6. 5Mn filler metal (LTT2) , (4) The fatigue life enhancing effect by using LTT2 with and without elongated bead applied to repair welding of boxing fillet welded joint with fatigue crack, (5) The fracture toughness of weld metal with LTT1 welding material, and so on.
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